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I remain unconvinced that my death has a fixed 100% probability, CMV.

Despite the overwhelming evidence that all human life so far has been subject to mortality, I still remain skeptical it's impossible to achieve immortality. There are already effectively 'immortal' lifeforms existing on Earth (eg. certain jellyfish, plants, lobsters)— why couldn't clever scientists eventually transpose the benefits to human life?

In pondering abiogenesis, I questioned the definition of life as we have it today. That would be a suitable starting place for immortality.

The examples I listed are immortal in the context of (semi)autonomous existence independent of their environments. Though they are not self-aware anywhere near the scale of human consciousness, they exist as independent agents in the objective shared reality we call "the universe". I wish to maintain this autonomy indefinitely. Whether I retain or shed off my biological characteristics (eg- cellular biology, endoskeleton, nutritional requirements, mandatory waste removal, etc) is completely inconsequential.

So, we'll go with "cyberman" type conversion. Where we take your brain, and plop it into a robot body.

"You" are then defined as your lifetime of experiences, which I suppose isn't a bad definition. Under that notion, you could exist until the heat death of the universe, or the more likely faulty software upgrade that deletes you cause somebody spills mountain dew on the server.

Hmm, even then not quite. Becoming an autonomous cyborg that retains all experiential memory is on the right track but not specifically what I had in mind. I wish to become "posthuman". A robotic-human hybrid that effectively curtails the unnecessary biological restraints while retaining all knowledge and wisdom of the host consciousness within the original organic body.

I also desire to stop the heat death of the universe, that's a distant goal though.

In theory, given the advanced technology, it would be possible to create a computer programme and robotic body which could simulate your mind and body, but it wouldn't be conscious in the way that you are conscious, it would only appear to others as if it was you ... it would still only be a machine

Research has been going on for a while as to how life can be extended beyond natural means so in the next few decades to the end of the century we should have made some headway.

But anyone who is on the Earth now WILL die, no technology or biological intervention can stop that. Any discoveries either won't be made in time or will not be available to the public (for obvious reasons). Not only this but that would mean that everyone on the planet would have to stop reproducing, you can't not die and keep having offspring, it simply doesn't work like that.

Many of the organisms you speak of have such a long life because of the low speed at which they grow, the habitat they live in or because of their basic body design.

But let me be very blunt, while this may be possible in the distant future you, I and everyone who reads this comment will die, of that i am certain.

EDIT: For your information a immortal organism is called a Darwinian Demon.

First of all, whether or not this is true depends on how stringently you mean "100%". If we get right down to it we can't know that we're not, say, living in some sort of computer simulation; if that's the case the "real" world could be anything you could imagine with any sort of arbitrary physics and rules. Nothing (with perhaps the exception of math and logic) can be known for sure. But, that makes for a boring argument. So let's start with the premise that reality exists and is pretty much how we observe it. Not too much to ask, right?

The first thing you'll realize when you start thinking about this is that to have a non-zero chance of dying you have to live forever. We're not talking about just living indefinitely long, replacing organs as you go and whatnot, but instead I should be able to name any time in the future and you'll still be around. Let's take a look at what that will take.

100 years: I'll assume you're in your early twenties right now so I have a number to work with. The longest living person that I'm aware of was Jeanne Calment who lived to the age of 122. So, if you want to live another 100 years, you could maybe do it just with good genes and good luck. We're only looking for a non-zero chance, so we're doing good so far.

200 years: Congratulations! You've lived another 200 years and managed to break all records of human lifespan previously known. To get to this point unprecedented medical advances have been made. New organs can be grown replaced as you need them, and methods have been devised to keep your brain cells healthy, or at least to replace them bit by bit. Or maybe you do get a brain replacement every now and then, but your old memories, personality, intelligence, etc. are imprinted on it. Would that still count as you? For the sake of argument let's say sure, why not.

Almost as important as the advances in medical technology is your access to it. Perhaps this tech is available only to the rich and influential, or maybe it's so cheap and easy everyone can use it. In any case, you've managed to discover the fountain of youth, and you have a long life ahead of you.

10,000 years: A lot has changed in your lifetime. You're one of the oldest humans alive, having been lucky enough to be in the first generation that had access to effective immortality. Aging and disease are distant memories. You've managed to live through the strife caused by the end of death. Perhaps that elixir of immortality is available to only a select few, or perhaps humanity has spread beyond Earth to cope with an ever-growing population, or maybe childbirth is strictly controlled. Whatever happened society lives on, and you with it.

100,000 years: You've managed to go a thousand centuries without your head getting crushed under the back wheels of a bus. Kudos.

1,000,000 years: A million years. Wow. How much memory can the human mind hold, anyway? Do you remember your childhood, your first kiss, the face of your parents? Perhaps you have some sort of external memory. How recognizable would you be now to yourself in the year 2013AD? Are you still human, even? Whatever you are, let's say that you're still you, and you've lived this long.

You've seen the rise and fall of countless civilizations. Most of human history is in your mind. The invention of agriculture and the city happened a mere 10,000 years before you were born; at this point, that's pretty much a rounding error in your age.

109 years: The Earth is about 5.54 billion years old now. You've been around for 18% of that. When you were born there had been five major mass extinction events in Earth's history. Has another one happened by now? Perhaps a giant comet or meteor has struck the Earth in your lifetime, shrouding it in a cloud of debris that blocked the sun. Maybe a nearby star went super nova and bathed the Earth in gamma radiation, driving you and everyone else underground. Whatever has or hasn't happened, humanity must have god-like technology by now for you to have survived this long. We're definitely in the realm of science fiction now, but you said 100% certainty, so why not?

3 x 109 years: The Milky Way and the nearby Andromeda galaxy merge. You've seen Andromeda grow in the night sky from the little smudge it is today to a giant, sky filling wonder. Don't worry, galaxies are mostly empty space, so it's very unlikely that our sun will be hit by another star. You and whoever else is around will have to think of a name for the new galaxy that forms.

5 x 109 years: You're about half as old as the Earth now and the sun is dying. As it burns through its hydrogen fuel it begins to fuse helium and heavier elements. The sun expands and swallows up the planet Mercury, then Venus. You had better hope that there was a well funded space program sometime in the last few billion years because Earth is not a fun place right now. The oceans have boiled away and the surface is a scorched desert, to say the least. At noon the giant, red sun fills the entire sky from horizon to horizon. Hopefully you've invested in a nice retirement home on Europa.

1010 years: You're about half as old as the universe and Earth (and the rest of the solar system) is long gone. Has the problem of traveling faster than light ever been solved? Can you zip between stars with your warp drive, or do you just accept that trip will take a while? You've certainly got the time to travel, and if you're going at relativistic speeds it doesn't even seem to take that long to you. By now lots of good books have likely been written, so hopefully you'll have something to keep yourself busy on your voyages between stars.

1011 years: The galaxies in the Local Group begin to merge together into one giant galaxy. Guess you'll have to come up with yet another galaxy name.

1012 years: Half-Life 3 is released. It doesn't live up to your expectations.

2 x 1012 years: Remember how you had to keep coming up with galaxy names? Well, the universe is constantly expanding and all other galaxies have receded beyond the edge of the observable universe. So, since there's only galaxy sitting in the middle of a black emptiness that stretches billions of light years in each direction it seems kind of redundant to bother naming it. When you meet new alien lifeforms and civilizations you try to tell them that the universe used to be full of galaxies just like the one you're in now, but it seems a little farfetched to them.

3 x 1012 years: You and whatever's left of humanity and the other races you've met clearly have amazing powers to have lasted this long. You may as well get a hobby. Why not find a planet with primitive intelligent life and convince them you're God? Get a few friends together and get followers on different continents, and see whose worshipers dominate the world. Best RTS ever.

1014 years: Star formation ceases. The stars that currently exist burn out one by one, leaving dimly glowing dwarf stars, fast spinning pulsars, black holes, etc. The night sky (assuming you're even on a planet right now) grows darker with each passing aeon as the stars wink out of existence. You've been around a long time, and you start to feel an emotion you almost forgot the existence of; an existential fear of your ultimate fate.

1015 years: You're having a hard time finding a welcoming planet. The ones that haven't fallen into their parent stars have been flung into interstellar space, drifting forever in the cold darkness. Perhaps you and what's left of the other intelligent races have undertaken a massive engineering project to keep the light of life burning in a dying universe. You and the others build an artificial star at the centre of a Dyson sphere, a solar system sized construct surrounding your new sun. This is the last bastion of civilization and intelligent life, a flickering candle in the infinite darkness. Memories of everything and everyone that ever was is stored in vast libraries. You and the other immortals try to discover new physics to stave off the inevitable.

1018 years: You stare into the abyss, wondering if there are other bastions of civilization like yours that exist beyond the edge of the observable universe.

1020 years: Similar to the fate of the planets, stellar remnants are flung from the galaxy or begin falling into black holes. The One Galaxy grows smaller and denser, increasing the speed of this process. You and the Immortals are mindful of this and carefully plot the trajectory of your home. Perhaps you're somehow finding fuel for it to keep the star at its centre burning, or maybe you have to keep making new ones. As the last galaxy dies, you're concerned that you can't keep this up forever. You continue your study of physics; no new discoveries have been made in aeons, but you keep looking for loop-holes in the laws of nature that might save you. Many others have decided this is futile and have accepted their fate, leaving your collective to drift lifeless among the remains of the stars. You press on.

1040 years: You know protons, one of the subatomic particles that (along with neutrons and electrons) make up the atoms and molecules of all matter that you interact with? Most of them are gone by now, having decayed away in a slow but inevitable process. All regular matter that's left is a rare resource. If you've somehow, miraculously, against all odds made it to this point, you're most likely alone. Everything is cold, dark, empty, unforgiving.

10100 years: All that's left in the universe is you (somehow) and black holes. How are you even still alive? The vast majority of your existence, so much so that everything else is barely even worth mentioning, has just been you floating in darkness with nothing but black holes for company. Even they are starting to vanish as they evaporate through Hawking radiation, shrinking in mass and then winking out of existence.

Beyond: There are still some photons, electrons, and other things flying about, but the universe is so vast and empty that they hardly ever interact with each other. It's uncertain what the future holds at this point, but you won't be around to see it. Some of the electrons that were once part of you are still around I suppose, somewhere, but it's impossible at this point that anything that could be considered "you" could remain. Perhaps other universes exist or will come into existence, and if there are an infinity of them then some entity very much like you could very will exist in them, but the "you" that you are now will be gone, irrecoverably, forever. The light of life in the universe has guttered and been extinguished.

tl;dr: Maybe you can beat cancer and AIDS and aging and go live among the stars, but you'll never escape entropy.

Edit: This has been linked in a couple of places and is generating a lot of interesting discussion. Since I can't really respond to everyone I'd just like to say here that I thank everyone for their kind words and I'm really glad that so many people are enjoying this and the discussion around it.

More info:

The Last Question by Isaac Asimov is a wonderful short story that has been linked to by a few users in response to this.

Bravo! That was the most fun read I've had in ages. Dw, the gold is on the way!

Yeah, the entropic heat death of the universe is a rather difficult problem. [Greatest understatement of all eternity? ahahaha] Regardless, if I wish to be truly immortal I must overcome it somehow. If the life of this universe is convincingly finite, I will move. However that is the last-case scenario. I will spend my eternity learning how to reverse entropy, starting today. This is a pretty nice headstart, wouldn't you agree?

Thanks, it was quite fun to write! The heat death problem really is a limiting factor for immortality, isn't it? To solve it, our most fundamental understanding of physics (things like the laws of thermodynamics, conservation of energy, etc.) would likely have to be wrong, and whatever replaces it would have to be consistent with being able to somehow create the eponymous 'world without end'. Or maybe some more exotic theories would be able to solve the problem. If other universes exist within black holes, maybe you could find some way to visit them? Might be difficult to do without being ripped apart, or stuck in time, or who knows what.

If you're truly immortal I think some weird math comes into play as well. If you consider an infinite amount of time, then anything with a non-zero probability will happen. If any sort of accident that could kill you is possible, then it becomes inevitable. Really, this sort of thing is beyond my ken, but it's fun to think about.

If you consider an infinite amount of time, then anything with a non-zero probability will happen.

This is technically incorrect in a rather subtle way. First, you could have something with a nonzero but exponentially decreasing probability; if there's a 1/20 chance of something happening this year, and the probability is halved each subsequent year, then there's only a 1/10 = 1/20 + 1/40 + 1/80 + ...less than 1 probability of it happening over an infinite time span. [EDIT: What was I thinking? Probabilities don't add like that! Please ignore my miscalculation — which, fortunately, doesn't affect the main point — and read this comment for the correct calculation.]

Second, "zero probability" isn't the same as "impossible". Suppose the probability of something happening is 1/2 each year. Then the probability after N years of it not having happened is 1/2N. Over an infinite time span, the probability is exactly zero. Nonetheless, it is possible for a probability zero event to occur.

Here's an example that illustrates this: Consider the outcome of an infinite sequence of coin flips. What was the probability of getting those exact results in that order? Well, that's the same as the probability of doing the same thing again and getting the same results — i.e., the probability of flipping two coins infinitely many times and having them land the same side every time. But that's exactly 0, because the probability of the coins matching N times in a row is 1/2N. Therefore, the original event — getting that particular result from an infinite sequence of coin flips — had probability zero. However, we were guaranteed to get some result, so this is a situation where every possible outcome individually has zero chance of occurring. (Note, however, that this relies in a critical way on there being infinitely many coin flips; in a finite, discrete probability space, this counterintuitive behavior cannot occur.)

Hm, I'm afraid that I had no intention of coming across as facetious at all. For what its worth, I also had no intention of appearing narcissistic.

I simply want to live forever, and I want all my loved ones to live forever too. "Loved ones" include every sentient entity across the entirety of the universe. I will leave noone behind in my quest to spread immortality and enlightenment.